1. Field of the Invention
The present invention relates to solid electrolytic capacitors.
2. Description of Related Art
FIG. 9 is a cross-sectional view of a conventional solid electrolytic capacitor 1. The solid electrolytic capacitor 1 comprises a capacitor element 7 covered by an exterior resin 11, and the solid electrolytic capacitor 1 also comprises on its lower surface an anode lead frame 8 and a cathode lead frame 9 as external electrodes.
An anode body 2 is a sintered body of a valve action metal. On a peripheral surface of the anode body 2, sequentially formed are a dielectric oxide film 3, a cathode layer 4, and a cathode lead-out layer 5, and an anode lead 6 made of a valve action metal having a cylindrical form, quadrangular prism form or the like projects from a generally central part of the anode body 2 in the height direction to form the capacitor element 7. The valve action metal is a metal on which an extremely dense and durable dielectric oxide film is formed by electrolytic oxidation process, including tantalum, niobium, aluminum, titanium and the like.
A lower end surface of the anode lead 6 and an upper surface of the anode lead frame 8 have different heights, and therefore, the anode lead 6 and the anode lead frame 8 are electrically connected to each other via a pillow member 10 having a cylindrical form, quadrangular prism form or the like by, for example, laser welding.
Nowadays, downsizing and weight saving of electronic devices such as a computer, portable phone, digital camera and the like is advanced, and also advanced is downsizing and weight saving of solid electrolytic capacitors to be built in such electronic devices. Specifically, the form of the anode lead is shifted from the cylindrical form to the quadrangular prism form to lower the profile of the anode lead, thereby lowering the profile of the solid electrolytic capacitor.
FIG. 10 shows an anode section 12. The anode section 12 is formed by vacuum sintering of a compact of valve action metal powder and the anode lead 6 a predetermined part of which is embedded in the compact. The anode section 12 consists of the anode lead 6 and the anode body 2 which became a sintered body of the valve action metal.
FIGS. 11a and 11b are a top view and a front view of the anode section 12 after being sintered respectively. It is problematic because, as shown in FIG. 11a, a crack 30 occurs on a planting surface 22 of the anode body 2 in which the anode lead 6 is planted, and the crack 30 spreads from a boundary between the planting surface 22 and the anode lead 6, particularly adjacent to a corner part of the quadrangular prism, thereby increasing leakage current.